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Phylloxera: What is it?

Additional Fact Sheets on Phylloxera:

Contributing List of Authors: Ed Hellman. Oregon State University. This fact sheet and others on grape phylloxera were produced as a set by a phylloxera task force at Oregon State University: Bernadine Strik, Extension Berry Crops Specialist; M. Carmo Candolfi-Vasconcelos, Extension Viticulture Specialist; Glenn Fisher, Extension Entomologist; Edward Hellman, Extension Horticulture Agent; Steven Price, Post-doctoral Research Associate, viticulture; Anne Connelly, Master’s student, horticulture; and Paula Stonerod, Research Aide, horticulture. The authors of this fact sheet acknowledge the help and guidance of others on this task force.

History:

Phylloxera are native to the eastern and southern U.S. The pest was inadvertently introduced to France from North America in 1860. It was identified in the mid-1800’s and by the end of the nineteenth century had destroyed two-thirds of the vineyards on the European continent, all self-rooted Vitis vinifera.

Since that time, phylloxera have invaded most of the grape-growing areas of the world (Europe, New Zealand, Australia, South Africa, for example). It was introduced into California in the 1850’s from the eastern U.S. Phylloxera were identified in the Penticton area of British Columbia in 1961 and in eight sites in Washington State, one of which was a V. vinifera vineyard, in 1988. Phylloxera was also discovered in Oregon about 20 years ago. However, in 1990, this pest was discovered for the first time in “modern” commercial vineyards. In 1995, 10 infested vineyards were identified; there are probably many more than this infested in the state. Phylloxera are now found in every major grape producing region in Oregon.

Description and Life Cycle:

The grape phylloxera, Daktulosphaira vitifoliae (Fitch), is an aphid-like insect that feeds on grape roots. The adults are all females and they are extremely small–0.7 to 1 mm (1/30 to 1/25 inch) long and 0.4 to 0.6 mm wide. This pest is thus very difficult to detect (see Sampling Vines to Confirm the Presence of Phylloxera). Color of the adults varies with the food supply: on fresh vigorous roots they are pale green, yellowish-green, olive green, or light brown; on weakened roots they are brown or orange. Mature adults become brown or purplish-brown. Each female can lay as many as 400 eggs. Newly deposited eggs are lemon yellow, oval, and about twice as long as they are wide.

The rate of development of this pest depends on the grape root and vine phenology as well as numerous environmental factors including soil and air temperature and humidity.

Phylloxera overwinter on roots as small dark-colored nymphs (hibernants). In the spring when soil temperatures go above a critical level (about 45 to 65 F–from our research) and vine sap starts to flow, these nymphs begin feeding and molt to adulthood. The mature forms, which are females only, deposit eggs by asexual reproduction. In Oregon vineyards, the first eggs have been detected in June. Two to three generations per year have been seen here. Phylloxera are most numerous in late summer to early fall. Thus, it’s easiest to detect the insect by digging up grape roots at this time. At this time of year, the risk of spreading this insect is also the greatest (see Reducing the Risk of Phylloxera Infestation).

Newly hatched nymphs can leave the roots where they were hatched and travel on the soil surface, in cracks in the soil, or can climb the vine and be wind blown for considerable distances. These “crawlers” usually only leave a vine once phylloxera populations become high and there is feeding competition or when a vine is near death. In Oregon, above-ground nymphs have been detected on trunk wraps in July and August.

In late summer, possibly due to environmental or population conditions, some nymphs may develop wing pads and emerge from the ground as winged adult females (alates). The females usually fly to an upright surface (trunk, for example). They lay male and female eggs which hatch into male and female phylloxera that have no mouth parts but mate. The female lays a large overwintering egg; this probably overwinters in crevices on the trunk. This egg hatches into a female who feeds on the leaves of susceptible grape varieties creating a leaf gall. She lays eggs producing a population of nymphs. These can reinfest the root system or other leaves.

At the end of September, nymphs begin to hibernate and by mid-December all forms are hibernants.

The winged, or sexual stage of phylloxera has been found in Oregon; these were caught on sticky trunk wraps in July and August. It is not known if winged phylloxera can complete their life cycle on European wine grapes–if they can, then the rate of spread of this pest will increase dramatically. However, we do know that the winged form can complete its life cycle on the foliage of American grapes (i.e. ‘Concord’, or a rootstock) or French-American hybrids (i.e. ‘Marechal Foch’). Look for leaf galls on susceptible vines–not brown or white fuzz on the leaf bottom like those produced by erineum mites but light green galls on the underside of the leaf. These are a symptom of the above-ground portion of the phylloxera life cycle.

Injury:

Principal damage to Vinifera grapevines is caused by phylloxera inhabiting and feeding on roots. It is believed that, when feeding, phylloxera inject poisonous saliva that causes swelling of roots. Feeding is generally on the tips of the rootlets causing yellowish-brown, hook-shaped swellings or galls (nodosities) to form which may curve and bulge around the insect body. In most cases, the swelling stops rootlet growth and the infested portion eventually dies. Feeding on larger roots causes rounded swellings (tuberosities) which give the root a “warty” appearance. These tuberosities may also decay, further weakening the vine.

Root injuries impair the absorption of nutrients and water, causing a decline in vine vigor and productivity. Decomposition of roots is also hastened by secondary infection by fungi and by the feeding of other insects and mites.

Injury to the above-ground portion of the vine is an indirect result of root damage and thus the symptoms are identical to some other pest problems such as Armillaria (oak root fungus), gopher damage, or nematodes (may also cause similar root symptoms) and environmental problems such as severe water stress and winter injury (see Sampling Vines to Confirm the Presence of Phylloxera).

The severity of the infestation may differ because of variety, vine age and vigor, soil condition, and drainage.

Vigorous vines resist phylloxera attack better than do weak plants. Differences in vigor can be due to site differences, but also varietal differences.

Infested vines live longer in fertile, deep, well-drained soil than in shallow soil or soil with poor drainage. Vines growing in heavy, shallow soils appear to succumb to the infestation most rapidly. Fine-textured soils, such as clay, are generally more favorable to infestation than light sandy soils, which appear to be almost immune to phylloxera. Heavier soils contract and crack when drying, and these openings allow the insect to crawl to and infest root systems.

Rate of spread in Oregon has ranged from 2X (doubling in size of the infestation annually) to 10X (a site where the pest came in on infested plant material). Managing an infested vineyard, therefore, is a challenge. See Managing a Phylloxera-infested Vineyard for more information.

There is no control for phylloxera that eradicates the pest in an infested, susceptible vineyard. The only method of control is to plant vines grafted to a resistant rootstock. See Phylloxera-resistant Rootstocks for Grapevines for more information.